Nuclear reactor and irradiating system



June 18, 1963 R. s. STONE ETAL 3,094,470

NUCLEAR REACTOR AND IRRADIATING SYSTEM 3 Sheets-Sheet 1 Filed Nov. 12, 1959 B {2%, M, M1 8 m, [12 5 June 18, 1963 R. s. STONE EI'AL 3,094,470

NUCLEAR REACTOR AND IRRADIATING SYSTEM Filed Nov. 12, 1959 3 Sheets-Sheet 2 jvw o, M1 wn! 821 a. 5

June 18, 1963 R. s. STONE EI'AL 3,094,470

NUCLEAR REACTOR AND IRRADIATING SYSTEM Filed Nov. 12, 1959 3 Sheets-Sheet 3 United States Patent Oil ice 3,094,470 Patented June 18, 1963 ware Filed Nov. 12, 1959, Ser. No. 852,505 6 Claims. (Cl. 204-1542) The present invention relates generally to neutronic reactors and more particularly to a neutronic reactor which is especially useful for producing radioactive isotopes.

Radioactive isotopes are being used in increasing quantities in research, industry and medicine. Radioactive isotopes of half lives longer than 12 hours are mainly being supplied by the Atomic Energy Commission. Unfortunately, radioactive isotopes having half lives of less than 12 hours generally cannot be shipped from Atomic Energy Commission production plants to a utilizing organization in time for practical use. There are roughly about 60 short-lived isotopes which can be easily produced by an isotope-producing reactor facility which are, in effect, unavailable for commercial use. Such shortlived radioactive isotopes have certain inherent advantages, particularly in tracer techniques, over longer-lived isotopes. In this connection, in medical and biological uses of radioactive tracers, it is desirable to hold to a minimum the radiation dose administered to the system in which the tracer is used. It can be shown that, for a given activity at the time the radioactive measurement is made, the smallest dosage is incurred by the system when the mean life of the radioactive tracer is equal to the time interval between the injection of the radioactive isotope and its measurement. Also, it is possible to use radioactive isotopes for certain production control applications only if the residual activity a short time after production is sufliciently low. Certain short-lived radioactive isotopes can be produced with every little longer-lived contamination so that decay to a negligible background takes place within a day or two. A further advantage is that short-lived radioactive wastes are far easier to dispose of than longerlived radioactive wastes.

Accordingly, it would be desirable to have available short-lived radioactive isotopes for commercial uses. This may be accomplished by producing the particular radioactive isotopes in an isotope-producing facility such as a neutronic reactor on the premises of the utilizing organization.

Additional advantages arise from having a neutronic reactor on the premises which is capable of producing radioactive isotopes. In this connection, regardless of the length of the half lives of the radioactive isotopes produced by the reactor, such radioactive isotopes generally would be more readily available than if they had to be obtained on order from some central organization, such as the Atomic Energy Commission. Furthermore, the utilizing organization would have greater privacy as to the nature of its work, and better control of the chemical and physical form of the samples which are irradiated. In addition if a large number of isotopes are made, it may be less expensive to make them in ones own reactor than to buy them. 7

To be a useful isotope-producing reactor which operates on the premises of a utilizing organization, the reactor should be designed to allow continuous or intermittent operation with equal case, but capable of being operated by relatively unskilled operators. It should provide for simultaneously irradiating a large number of samples of various sizes and shapes. The samples should be insertable and removable from the reactor while the reactor is in operation and with minimum handling time. The reactor should have sufficient power so that a wide range of radioactive isotopes can be produced, including the short-lived radioactive isotopes which, as indicated above, have heretofore been unavailable to industry; and finally, the reactor should be available at a relatively moderate cost.

An isotope-producing reactor capable of satisfying the foregoing requirements is described in Stanley L. Koutz et a1. patent application, Serial No. 744,364, filed June 25, 1958, now Patent No. 3,072,549, and assigned to the assignee of the present invention. The present invention is directed to an improvement of the invention set forth in Serial No. 744,364.

It is a primary object of the present invention to provide a novel method and apparatus for simultaneously and uniformly irradiating a plurality of samples in an isotopeproducing neutronic reactor. Additional objects and ad vantages will be apparent from a study of the following description, and from the accompanying drawings, wherein:

FIGURE 1 is a sectional view of a reactor constructed in accordance with the present invention, with parts thereof broken away;

FIGURE 2 is an enlarged plan view of the upper surface of the rotary specimen rack shown in FIGURE 1, with portions thereof cut away to show certain of the inner mechanisms of the specimen rack;

FIGURE 3 is a cross sectional view taken along the line 33 of FIGURE 2; and

FIGURE 4 is an enlarged perspective view of the specimen rack operating and indicating mechanism used in connection with the reactor shown in FIGURE 1, with portions cut away to show certain of the interior mechanism thereof.

The illustrated embodiment of the invention comprises a neutronic reactor including a reactive core, a reflector extending about the core, a movable member or specimen rack in the reactor for supporting a plurality of specimens to be irradiated, means for removing a specimen from the specimen rack at a predetermined position in the reactor, and means for moving the specimen within the specimen rack in the predetermined position. While many different types of reactors may be utilized for purposes of this invention, it is preferred, but not essential, that the reactor core be located in a tank which is disposed Within a pit in the ground, so that effective shielding against radiation may be afforded in an economical manner, without resorting to expensive above-the-ground shielding structures. The tank is filled with a suitable liquid such as water which serves as a moderator, coolant and shielding. Cooling means may be provided for the fluid within the tank for regulating the temperature of the core. Suitable pickup means are furnished to remove the specimens from the reactor while it is in operation. Also furnished in the reactor is a control system for regulating the power level of the reactor.

The core of the reactor may be of any suitable construction. However, it is preferable if the core is designed so that the reactor is inherently safe, i.e., it will not be damaged by an unexpected and sudden surge in neutron multiplication. In the illustrated embodiment, the core of the reactor is designed, in combination with the remaining components of the reactor, to have a high prompt negative temperature coefiicient of reactivity, i.e., one which does not require the flow of heat from one region to another in order for it to come into play. This is responsible for the great safety of the present reactor during its operation.

Now referring particularly to the drawings, the reactor, designated by the reference numeral 20, includes a core 21 disposed near the bottom of a reactor tank 22 which is filled with a liquid 23. The core 21 includes a plurality of fuel elements 24. Disposed in the core 21 are or other reinforcing material.

control rod assemblies 25 which are operated by suitable tion facilities including a movable specimen rack 28 are provided in the core 21 and reflector 27, for irradiating specimens at preselected radiation levels.

Reactor tank 22 is located in a generally cylindrical pit 30. The pit 30 may be constructed by standard construction methods, with the hole lined with concrete, steel In the particular assembly illustrated, the lining 31 of the hole is concrete. The depth ofthe reactor tank 22 is controlled by the amount of liquid shielding desired above the reactor core 21 which is Within the tank 22. The Width of the reactor tank 22 is controlled by the diameter of the reactor core 21, the size of the refiector127 and the shielding required to reduce the neutron activity to a desired value at the boundary of the tanlc. Reactor tank 22 is preferably constructed of a materialhaving a low neutron capture cross section. Since the reactor tank 22, is designed to contain liquid such as water, aluminum is preferred in order to minimize corrosion problems and to also reduce costs of construction. Reactor tank 22 is cylindricalin form with an open top of suitable dimensions to tit inside the, pit 30. The bottom of reactor tank 22 is supported in position above a horizontally extending concrete base '32 which forms the bottom of pit 30. The bottom of the tank 22 rests on a platform comprising a flat, generally circular plate 33 preferably of aluminum. The plate 33 in turn is supported on a series of lhorizon'tal'aluminum beams 29. A-porous fill, s'uchas gravel,is" placed in an annular space 34 between the wall of the reactor tank 22 and the Wall of the pit 30. Any water which may leak into the annular space 34, either from the reactor tank 22 or inwardly from the outside of the concrete lining 31, is collected in a's'pace .35 at the bottom of'the pit 30. .A suction line (not shownl'm'ay. be run downthrough the annular space 34 to remove any water which'may collect. v

Reactor tank 22 is' .disposed" within the ground in'the described manner so that the ground itself acts as a natural protective shielding m'eans'fo-r the reactor. Accordihgly, construction costs are reduced, since expensive above-the-ground shielding structures are obviated.

A horizontal shelf. 36 is preferably provided atthe upper .end of the pit 30Ifor themounting of the control rod winch'm'echan'ism. The outeriperimeter' of'the shelf 36 is illustrated. asbeing substantially square, however, the Tspec'ific contour of the perimeter of the shelf is unimportant. The surface of the shelf 36 i's at a suflicient [depth from floor level 37 to accommodate the height of the winch mechanisms. to the concrete at each edge .of the perimeter of the'shelf ...35'for support of a two seems cover 40 over the pit 30. Ifdesired, a grate may be' used for the cover 40 so that A channel 38 may be attached the reactor can be visually observed during operation. Within the lower portion of reactor tank 22'is located the core 21 which is in the general form of a right circular cylinder and oomprises a lattice of generally vertically extending fuel elements 24 held in spaced relation by grid plates or-the like. I

As; seen in l, the fuel elements 24 in the core zl'extend in a generally vertical direction and are generally uniformlyspaced in concentric circles. T The illustratedreactor providespositions for eighty-six fuel p the number of fuel elements 24 as comparedto the' dummy elements will vary considerably, depending upon the general design and-dimensions of the reactorand particular arrangement of the'fuel elements' 24.

In the illustrated embodiment, three symmetrically posi- '4 tioned control rod assemblies ZS are provided, one of which is shown. Each of these control rod assemblies 25 includes a control rod which is designed to perform a different function in the reactor so as to achieve both range and accuracy of control. A so-called shim safety rod is used for coarse control of the reactor. The shim safety rod has a; fairly large reactivity equivalent. A regulating rod having a smaller reactivity equivalent is provided for fine control of the reactivity. The shim safety rod and the regulating rod each have a reactivity equivalent great enough to shut down the reactor. A third rod having a large reactivity equivalent which may be equal to c that of the shim safety rod is used as a safety rod. -It has a large enough reactivity equivalent to shut the reactor down and is used to shut down the reactor quickly in the event of an emergency. V H 7 While the center of the core 21 may also be provided with a control rod assembly, in the illustrated embodiment a tubular irradiation thimble 4 2 is run vertically through an enlarged-central hole in the lower grid plate of the core, through the central hole of the upper grid plate and through thereactor tank 22 to the top thereof.

. This thimble or glory hole 42'is at a point of n eutron flux in the reactor. The thimble =42 is useful for 25.

isotope production, pile-oscillation experiments, and danger-coefiicient experiments. g

The core :21 is centrally located with respect to the reflector 27. Any material having good scattering properties and a low neutron absorption cross section, such as graphite, beryllium or beryllium oxide, can be used to construct the reflector 27 In the illustrated embodiment a plurality of suitably shaped graphite blocks 44 are used. Thereflector 27 is substantially cylindrically shaped with a hollow circular center and is completely encased in a water-tight can 46.

The diameter of the reactor tank 22 is made substantially larger than the outer diameter of the reflector 27 to provide an annular space between the reactor tank 22 and the reflector 27. This space, when filled with water, increases'the neutron flux available in the reflector :27, While using the minimum possible size reflector 27, In addition, this annular space facilitates the installation and removal of the reflector assembly 27. The graphite blocks 44 are encased in the water-tight can 46 so as to prevent Water, from entering the reflector material and decreasing the reactivity of the reactor.

Referring to FIGURES l, 2 and 3, the rotary specimen rack 28, which is located in an annular recess 48 in the reflector 127, is constructed so that specimens can be loaded and unloaded conveniently during operation, and so that such specimens are uniformly irradiated. The rotary specimen rack '28 includes a plurality of spaced cups 50 which are attached to and extend below a flat, horizontally extending, rotatable ring 52. The cups 5% serve as holders for specimen containers. .In the illustrated embodiment, the cups 50 are each in the form of a cylindrical tube closed at its lower end. The cups are attached so as to extend downwardly from a series of spaced holes 54 in the ring 52. The number of cu-ps 50 is dependent upon the requirements of theinstallation. In the illustrated embodiment, forty cups are disposed at equal intervals around the ring 52. The upper surface of the ring is countersunk at each hole 54 so as to guide the specimen containers into the cups 50.

The ring 52 and cups are rotatably supported within a housing 56 by a bearing structure 58. Any bearing structure which allows the ring 5-2 to be freelyrotatable relative' to the housing 56 may be used. In the illustrated embodiment, a ball bearing ring structure'is' used. The ball bearing ring structure includesjan inner race 60, an outer race 62, and a plurality of balls64 rotatably engaged therein. The outer race 62 is fastened securely to a mating recess 66 at the lower inner corner of the ring 52. The inner race 60 is fastened to a mating recess 68 Within a bearing support ring 70, which in turn is securely attached to the housing 56, preferably by welding. The ring 52 is rotatable from the top of the reactor to continuously move the cups 50 around the reactor core, and also to successively bring each cup 50 to a position under a single vertically extending delivery and removal pipe 72.

The housing "56, previously mentioned, is of watertight construction and encloses the internal mechanism of the specimen rack 28. The housing 56 is designed so as to substantially occupy the annular recess 48, and thus minimize the introduction of water into the reflector volume. The housing 56 may be removed from the reactor tank 22 without disturbing the core 21 or reflector 27.

In the illustrated embodiment, the housing 56 is formed by welding or the like and includes a stepped tubular inner wall 74, a tubular outer wall 76, a ring-shaped bottom wall 78, and a ring-shaped top wall 80. The top and bottom portions of the inner wall Mare of different diameters. The top portion which is of smaller diameter is connected to the bottom portion by a ring 80a which forms a shoulder which rests .on the reflector 27 when the housing 56 is properly positioned in the reactor. Lifting lugs 82 are attached to the upper portion of the inner wall 74 .of the housing '56 to facilitate the handling of the rot-a'ry specimen rack 28.

A pair of openings 84 and 86 are provided in the top wall 80 for the delivery or removal of specimen containers and for enclosing a drive shaft and a positioning shaft 88 and 90 respectively (described subsequently). In the illustrated reactor the openings 84 and 86 :are diametrically opposite to each other. Vertically extending tubes or pipes 72 and 92 which connect with the openings 84 and 86 extend from the top of the housing 56 to the top of the reactor tank 22. The pipes 72 and 92 are preferably formed in mating sections for ease of assembly. The delivery and removal pipe 72 is slightly larger in diameter than that of the cups 50. The lower end of the delivery and removal pipe 72 extends into the housing 56 and is attached therein to a suitable supporting member 94.

The pipe 92 which encloses the drive shaft 88- and the positioning shaft 90 is of larger diameter than that of the delivery and removal pipe 72. A bearing plate 96 for supporting a sprocket 98 and the positioning shaft 90 extends across and is fastened to the inside of the housing 56 at the lower end of the pipe 92. The bearing plate 96 contains two vertically supported bushings 100 and 1192 for the positioning shaft 90, and for the drive shaft 88, respectively.

A roller chain 1414 and sprocket 98 are used to rotate the ring 52 and cups 511. The chain 104 extends along the upper surface of the ring 52 and is fastened at spaced intervals thereto. Any suitable fastening means can be used to secure the chain 104 to the ring 52, such as riveting.

The sprocket 98 is fastened to the lower end of the drive shaft 8% beneath the bearing plate 96. The sprocket 93 engages and drives the roller chain 104. Thus, the rotation of the drive shaft 88 causes a correlative rotation of the ring 52. A collar 106 is attached to the drive shaft 88 above the bushing 102 to maintain the sprocket 98 in vertical alignment with the roller chain 104. The drive shaft 88 extends upwardly through the pipe 92 to the top of the reactor tank 22. As seen in FIGURE 4, the upper end of the drive shaft 88 extends through a pair of vertically spaced bearing plates 108 and 11 i. Attached to the upper end of the drive shaft 88 is a turning means, such as a hand wheel 112.

A positioning hole 114 is drilled in the ring 52 adjacent each cup 561 to insure proper positioning of the cups relative to the delivery and removal pipe 72. The holes 114 are so located that whenever the positioning shaft 94} drops into a hole 114 one of the cups 50 is in alignment with the delivery and removal pipe 72. The holes 114- are located on the upper surface of the ring 52 and are of a diameter such that the positioning shaft 90 may be slidably engaged therein. The positioning shaft extends through the pipe 92 to the top of the reactor. Preferably, the positioning shaft 90 is in more than one section for ease of assembly. The upper end of the positioning shaft extends through the bearing plates 108 and 110. A suitable gripping means, such as a handle 116 is attached to the upper end of the positioning shaft 90.

The positioning shaft 90 includes a pair of vertically spaced, horizontally extending pins 118 and 120 located adjacent its upper end which coact with the bearing plates 108 and 1110 to prevent excessive withdrawal of the positioning shaft and to maintain the positioning shaft out of engagement with the holes 114 during the period that the specimen rack 28 is rotated. The lower pin 118 is positioned below the lower bearing plate 108 a distance such that when the lower end of the positioning shaft 90 is raised above the surface of the ring 52 to permit the specimen rack 28 to'rotate, the lower pin 118 will abut against the lower surface of the lower bearing plate 108. The upper pin 120 is so located on the positioning shaft as to just clear a suitably slotted hole 122 in the upper bearing plate before the positioning shaft 90 is stopped by the lower pin. To lock the positioning shaft in its uppermost position, the positioning shaft is rotated until the upper pin is no longer in alignment with the slot 122 after which the positioning shaft 90 is released. The positioning shaft will be maintained in its raised position by the engagement of the upper pin 120 with the upper bearing plate 110.

If desired, a biasing spring (not shown) may be provided to urge the positioning shaft 90 in a downward direction so as to prevent accidental release of the positioning shaft when it is in engagement with one of the holes 114.

To indicate the position of the ring 52, the drive shaft 88 is connected through a suitable gear train 124 to an indicating pointer 126. The gear train includes a pinion gear 128 attached to the upper end of the drive shaft 88, a pair of idler gears 130 and 132 which are attached to an idler shaft 134 and a spur gear 136 attached to an indicator shaft 138 on which the pointer 126 is mounted. The idler shaft 134 and the indicator shaft 138 are journaled in suitable bearings (not shown) located in the bearing plates 110 and 108. The indicating pointer 126 is arranged to move across an indicating dial 140 as the drive shaft 88 rotates the ring 52. The indicating dial 140 is suitably calibrated so as to indicate the positions of the ring 52 where the cups 50 are in alignment with the delivery and removal pipe 72.

A housing 142 which is suitably supported above the reactor tank 22 on the channels 38 is provided for supporting the bearing plates 108 and 110 in spaced apart relationship and for enclosing the bearing plates 108 and 110, and the gear train 124.

Thus it is seen that means are provided for manually indexing the cups 50 with respect to the delivery and removal pipe 72 for exchange of samples in the reactor. In order to assure uniform irradiation of the samples when in the reactor, there is also provided means for continuously rotating the sample supporting ring 52 at a uniform, predetermined speed within the reactor. More particularly, there is provided a powered driving means which is suitably connected to the ring drive shaft 88 for effecting selective, continuous rotation of the ring 52 and the cups 50 supported thereby.

An electrical motor 144 is suitably mounted within the housing 142, and this motor has a drive shaft 146 fixedly mounting a pinion gear 148 which is in meshing engagement with the gear train 124 through the idler gear 130. Preferably, the motor drive shaft 146 includes a slip clutch 149, or the like, to permit rotation of gear 148 when the motor is turned off and manual control handle 112 is used. An off-on switch control, indicated at 151, is provided for the 'motor 144 and this switch is located on the upper surface of the housing 142. Consequently, once the desired number of samples are placed in the cups 50, which are individually indexed with respect to the delivery pipe 72 through manual rotation of ring 52 by operation of the manual control 112, the motor 144 can be operated to thereby provide continuous rotation of the samples about the reactor core at a selected, uniform rate of speed. This rotation of the samples is of con siderable advantage in effecting uniform irradiation of the samples, since the samples are thereby exposed equally to all sides of the reactor core wherein there is ordinarily some variation in the radiation intensity with respect to the several surfaces of the core.

If desired, suitable clutch mechanism (not shown) may be interposed between handle 112 and drive shaft $8 to selectively disengage the handle and prevent its rotation during motor operation of the drive shaft.

To prevent moisture from accumulating within the housing 56, one or more of the cups 50 may be provided with suitable perforations or openings 15% and these cups may be loaded from time to time with removable charges of a suitable drying agent such as silica gel. In one embodiment, for example, four spaced cups were suitably perforated, each with approximately forty inch diamerter holes. In addition, one of the cups included a central inch hole in its bottom wall to permit a sponge or other absorbent material to be lowered therethrough into contact with the bottom wall of the housing 56 to test for the amount of moisture within the housing.

In order to determine the positions of the perforated cups, the positioning hole 114 associated with one of the perforated cups is somewhat deeper than the rest of the positioning holes, so that when the positioning'shaft 90 drops to a lowermost position, it denotes that its perforated cup is in line with the delivery and removal pipe 72. Preferably, the indicating mechanism is adjusted so that at the position where the positioning shaft 5N) is in line with the deeper positioning hole 114, the pointers 126 will point to the dial 140 at some definite marking, for example, position number 1. Knowing the .relative positions of the other perforated cups, one can readily rotate the specimen rack to position any desired per-forated cup under the delivery and rem-oval pipe 72 by reference to the position of the indicating pointer 126 and dial 140.

Although shown and described with respect to particular mechanism, it will be apparent that various modifications might be made without departing from the principles of this invention.

We claim:

1. A method of irradiating a plurality of specimens in an isotope-producing neutronic reactor, comprising loading the specimenson a supporting member in spacedapart relation peripherally of the core of the reactor, continuously moving the supporting member completely around the core at a selected, uniform speed to expose each specimen substantially equally to all sides of the core during each revolution about the core, providing indicator means for indicating the positions of the specimens as the specimens are rotated about the core, and selectively removing said specimens from the supporting member.

2. A method of irradiating a plurality of specimens in an isotope-producing neutronic reactor, comprising loading the specimens on a supporting member in spacedapart relation peripherally of'the core of the reactor, continuously moving the supporting member completely around the core at a selected, uniform speed to expose each specimen substantially equally to all sides of the core during each revolution about the core, providing indicator means which is responsive to the position of the supporting member to indicate the positions of the specimens around the core and with respect to a position for loading and unloading the specimens on the supporting member, and selectively placing said specimens at the unloading position for removal from the core.

3. Apparatus-for irradiating a plurality of specimens uniformly in a neutronic reactor having a reactive core, said apparatus comprising a supporting member for supporting a plurality of spaced apart specimens to be irradiated about the periphery of the core, said supporting member being continuously movable completely around the core, a selectively operable motor means for operating unidirecti-onally at a selected uniform speed, connecting means between said supporting member and said motor means for continuously driving the specimens-on said supporting means completely around the core and exposing the specimens substantially equally to all sides of the core during each revolution about the core, and indexing means coupled to said supporting member for indicating the position of the specimens within the reactor as the specimens are moved therearound by said motor means.

4. Apparatus'for irradiating a plurality of specimens uniformly in a neutronic reactor having a reactive core and a reflector extending about the core, said apparatus comprising walls defining a recess in the reflector which extends in a circular direction, a flat ring supported adjacent the mouth of said recess, said ring being continuously movable completely around the core, a plurality of horizontally spaced-apart cups connected to and extending downwardly from said ring into said recess for holding a plurality of specimens to be irradiated, a selectively operable motor means for operating unidirectionially at a selected uniform speed, connecting means between said supporting member and said motor means for continuously driving the specimens on said ring completely around the core and exposing the specimens substantially equally to all sides of the core during each revolution about the core, and indexing means coupled to said ring for indicating the position of said cups within the reactor as the specimens are moved therearound by said motor means.

5. Apparatus for irradiating a plurality of specimens uniformly in a neutronic reactor having a reactive core and areflector extending about the core, said apparatus comprising walls defining a recess in the reflector which extends in a circular direction, a flat ring supported adjacent the mouth of said recess, said ring being co-ntinu ously movable completely around the 'core, a plurality of horizontally spaced-apart cups connected to and extending downwardly from said ring into said recess for holding a plurality of specimens to be irradiated, drive means extending from the exterior of the reactor to said recess, said drive means including a selectively operable motor means and means connecting said motor means in driving relation with said ring for effecting continuous rotation of said ring unidirectionally at a selected uniform speed completely around the core and exposing the specimens substantially equally to all sides of the core during each revolution about the core, and means for selectively positioning said ring so as to locate any selected cup at a predetermined position, said positioning means includ ing an indicator which is connected to said drive means for indicating the position of the cups relative to said predetermined position.

6. Apparatus for irradiating a plurality of specimens uniformly in a neutronic reactor having a reactive core and a reflector extending about the core, said apparatus comprising Walls defining a recess in the reflector which extends in a circular direction, a fla-t ring supported adjacent the mouth of said recess, said ring being continuously movable completely around the core, a plurality of horizontally spaced-apart cups connected to and extending downwardly from said ring into said recess for holding a plurality of specimens to be irradiated, drive means extending from the exterior of the reactor to said recess, said drive means including a selectively operable motor means and means connecting said motor means in driving relation with said ring for effecting continuous rotation of said ring unidirectionally at a selected uniform speed completely around the core and exposing the specimens substantially equally to all sides of the core during each revolution about the core, and means for removing a specimen from a cup at a predetermined position in said recess, manually operable means connected with said drive means for selectively positioning said ring so as to locate any selected cup at a predetermined position, said positioning means including an indicator which is connected to said drive means for indicating the position of the cups relative to said predetermined position, and a releasable locking means for said ring Which is engageahle therewith only when a cup is at said predetermined position for preventing the rotation of said ring.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Proceedings of the Second United Nations Interna- 10 tional Conference on the Peaceful Uses of Atomic Energy, vol. 10, United Nations, Geneva, 1958, pages 282-286. 

1. A METHOD OF IRRADIATING A PLURALITY OF SPECIMENS IN AN ISOTOPE PRODUCING NEUTRONIC REACTOR, COMPRISING LOADING THE SPECIMENS ON A SUPPORTING MEMBER IN SPACEDAPART RELATION PERIPHERALLY OF THE CORE OF THE REACTOR, CONTINUOUSLY MOVING THE SUPPORTING MEMBER COMPLETELY AROUND THE CORE AT SELECTED, UNIFORM SPEED TO EXPOSE EACH SPECIMEN SUBSTANTIALLY EQUALLY TO ALL SIDES OF THE CORE DURING EACH REVOLUTION ABOUT THE CORE, PROVIDING INDICATOR MEANS FOR INDICATING THE POSITIONS OF THE SPECIMENS AS THE SPECIMENS ARE ROTATED ABOUT THE CORE, AND 